1. Field of Invention
The invention relates to an optical device used in plane image input devices such as scanners or printers.
2. Related Art
Aside from drawing, video conferencing, multimedia and computer briefing, digital information is also important in business documents. Although paperless offices have not been realized, scanning has been used to generate electronic documents in business to reduce the use of paper.
The scanner has been a common input device because its operation is very simple. One only needs to open its lid, places the original document on its glass, and then covers the lid back. The rest is left to its operating software to control the scanning job.
The basic principle of the scanner is using a mechanical or electronic scanning module to read image points on the original document and then converting the points into a digital form. Since it casts light on the surface of the original document and converts the reflected brightness into digital information, it is called the photoelectric conversion. During the process that the image sensor reads the image signal on the original document, the light emitted from an illuminating source projects onto the surface of the original document. The light reflected by the original document goes through a lens to form an image on the sensor. Through the photoelectric conversion, it is converted into an output voltage proportional to the density of the image.
In recent years, all electronic devices become more compact, so are the scanners. However, the reflector for reflecting light forbids the minimization of the scanner volume. Therefore, it is an important issue how to minimize the volume of the scanning module. In addition to scanners, other plane image input devices such as printers also have similar problems.